🥮 mooncakes.io

    #Subscriptions

    The sub package models long-lived external signals that should feed back into your TEA update loop.

    Unlike Cmd, which runs once, a Sub stays installed until your app stops returning it.

    #Basic shape

    In Rabbita, subscriptions are usually returned from the subscriptions callback of create_state.

    ///|
    fn subscriptions(model : Model, emit : Emit[Msg]) -> @sub.Sub {
      if model.running {
        @sub.every(1000, emit(Tick))
      } else {
        @sub.none
      }
    }

    #Building subscriptions

    Use none when nothing should be active:

    ///|
    test "sub none" {
      let _ : Sub = @sub.none
    }

    Use batch to combine multiple subscriptions:

    ///|
    test "sub batch" {
      let _ : Sub = @sub.batch([none, every(1000, @cmd.none)])
    }

    #Emitting messages

    Event-based subscriptions usually work with emit.map(...), just like HTML event handlers.

    ///|
    enum Msg {
      Resized(ViewPort)
      MouseMoved(Mouse)
    }

    ///|
    fn subscriptions(_model : Model, emit : Emit[Msg]) -> @sub.Sub {
      @sub.batch([
        @sub.on_resize(v => emit(Resized(v))),
        @sub.on_mouse_move(m => emit(MouseMoved(m))),
      ])
    }

    RunningSub

    source
    pub(all) struct RunningSub {
      unload : (&
    Scheduler    ) -> Unit
      update_tagger : (Error) -> Unit
    }

    Scope

    source
    pub(all) enum Scope {
      Local
      Global
    }

    Sub

    source
    type Sub

    A long-lived subscription managed by the Rabbita runtime.

    Use subscriptions to listen to external signals such as timers, window resize, scrolling, keyboard input, visibility changes, or WebSocket events. Browser event sources are inert on native targets.

    SubLoader

    source
    pub(all) struct SubLoader((Error, &
    Scheduler    ) -> RunningSub?)

    Custom subscriptions loader.

    batch

    source
    fn batch(xs : Array[Sub]) -> Sub

    Combine multiple subscriptions into one.

    If multiple subscriptions use the same internal key, the later one wins.

    custom_sub

    source
    fn custom_sub(key : String, scope : Scope, payload : Error, loader : SubLoader) -> Sub

    Create a custom subscription

    every

    source
    fn every(ms : Int, cmd : 
    Cmd    ) -> Sub

    Repeatedly enqueue cmd every ms milliseconds.

    none

    source
    let none : Sub

    A subscription that does nothing.

    on_animation_frame

    source
    fn on_animation_frame(msg : 
    Emit    [Double]) -> Sub

    Subscribe to requestAnimationFrame ticks.

    The handler receives the browser timestamp for each frame while the subscription is active.

    on_key_down

    source

    Subscribe to document keydown events.

    The handler receives a normalized Keyboard value from @common.

    on_key_up

    source

    Subscribe to document keyup events.

    The handler receives a normalized Keyboard value from @common.

    on_mouse_move

    source

    Subscribe to document mousemove events.

    The handler receives a normalized Mouse value from @common.

    on_resize

    source

    Subscribe to window resize events.

    The handler receives the latest viewport width and height.

    on_scroll

    source

    Subscribe to window scroll events.

    This reports page-level scrolling on window, not scrolling of an inner element. The handler receives the current scroll offset and document scroll size as a Scroll value.

    on_url_changed

    source

    Subscribe to browser location changes.

    This is an app-scoped subscription. It is only active when returned from the root cell's subscriptions callback; if a non-root cell returns it, the subscription is ignored.

    on_url_request

    source

    Subscribe to captured navigation requests from @html.a(...).

    This is an app-scoped subscription. It is only active when returned from the root cell's subscriptions callback; if a non-root cell returns it, the subscription is ignored.

    on_visibility_change

    source
    fn on_visibility_change(msg : 
    Emit    [Bool]) -> Sub

    Subscribe to document visibility changes.

    The handler receives true when the document is hidden, and false when it becomes visible again.

    Source Files

    Powered by MoonBit

    Site sourceReport issuePackagesBuild queueSkillsStatistics

    © 2026 mooncakes.io